Put 2 in the first blank for water drop, and zero in the second for base height (this is a suggestion, default usually works okay too). There is no way to change the shape of the box, but we can trim the resulting stl in editing software. You can then place a box which will be your terrain.
Zoom to a place you want to map or enter your desired latitude/longitude in those fields. Here we will select an area for our terrain model. Go to this website: (another app that works in a very similar fashion and has better bathymetry capabilities is TouchTerrain).
Meshlab: this is another free editing tool, less oriented for printing and more towards making digital 3D models, but very useful for converting between file types Meshmixer: a free 3D model editing tool from Autocad There are two methods I suggest for printing 3D terrain models: first is using an app and the other is using a plugin (DEMto3D) in the open source software QGIS.
